1. Field of the Invention
The present invention relates to various medical devices used for the replacement of human joints. More particularly, the present invention relates to methods and apparatus for replacing human joints, in particular, hip joints. Additionally, the present invention relates to systems for automatically lubricating artificial joints.
2. Description of Related Art
Prostheses for the replacement of hip joints are already known. Originally, only the ball-end on the head of the femur could be replaced, but it has since proved possible to replace either part of the hip joint, that is to say, the acetabulum or the ball-end on the head of the femur.
The number of those living with hip prostheses is increasing more and more at the present time. The number of implanted artificial hip joints is estimated to be two thousand per day. The further increase of the cases into the millions is accounted for by the fact that the diseases of the hip joints due to wear are increasing numerically along with the rapid rise of the age of the population accompanied by a corresponding development of the medical technique.
Existing techniques for the carrying out of the hip replacement operation are extremely invasive. As such, the patient will require long periods of rehabilitation and long periods of hospital stay. Since a great deal of biological material is removed or replaced in the patient, a great amount of time is required for healing. Furthermore, the operative procedures are very time-consuming and very expensive.
Existing hip replacement techniques initially require the exposure of the femur. The hip must be dislocated so that the level of the neck resection can be measured proximally from the lesser femoral head based on the preoperatively templated measurement. In addition, the center of the femoral head is approximated and marked. A right angle retractor is used to judge the anatomical relationship for the later restoration of leg length and offset. The femoral neck cut is made by using a femoral broach as a template, by using the femoral neck cutting guide, or by using a femoral resection template. The neck cut is made slightly horizontal, which allows the use of the calcar planer to obtain a smooth surface for eventual flush collar-calcar seating.
Following the removal of the femoral head, a partial superior and anterior capsulectomy is performed to allow exposure of the anterior acetabular rim. Hohmann or similar retractors are placed over the anterior rim for retraction of the shaft anteriorly. Posterior and superior Charnley pin retractors are placed in the interval between the capsule and the labrum to allow complete exposure. The acetabular rim is then completely exposed by thorough removal of the acetabular labrum.
Once acetabular exposure has been accomplished, reaming is initiated. Reaming continues until concentric removal of all remaining acetabular cartilage and the exposure of punctate bleeding in the subchondral plate is achieved. The medial landmark for correct depth is the acetabular floor visualized through the acetabular fossa. A cup sizer corresponding to the last reamer used is placed on a handle and inserted into the acetabulum. The acetabular cup sizers are the same size as the actual implant and should fit snugly into the acetabulum.
It is then necessary to insert the cup. To correctly judge the appropriate component position, a down-sized acetabular sizer can be easily inserted and positioned into the acetabulum so as to allow removal of any overhanging anterior, posterior or superior osteophytes. Once these steps have been completed, the correct acetabular shell is locked into the acetabular positioner and driven into a fully seated position. Screws can then be used for supplemental fixation.
After the placement of the acetabular component, attention is then turned to the femur. The femoral canal is identified with a hand-held reamer. Power reaming is initiated with a conical reamer. The reamer is advanced slowly within the canal until the proximal cutting edge is at the level of the calcar. As the reamer is withdrawn, lateral pressure is exerted to insure proper lateralization within the canal. Reaming proceeds in one millimeter or two millimeter increments depending on the bone density. Once the appropriate conical reamer has been passed, rasping is initiated. The rasp should be oriented so that the mediolateral axis of the rasp is parallel to the anatomic mediolateral axis of the femoral neck. The rasp is impacted until it is slightly below the level of the initial calcar cut. Subsequently, larger rasps are used until the final rasping is completed with the appropriate size. With the proper size rasp in place, the calcar is planed flush by using the calcar trimmer. With the final rasp still in place, provisional heads/necks are selected to determine the appropriate neck length in order to restore the lateral offset. Trial reduction is carried out to assure that proper leg length and stability are achieved. The stem corresponding to the size of the final rasp used is threaded onto the stem inserter/extractor and impacted into a fully seated position. The collar should seat flush against the medial calcar and the lateral shoulder should seat against the femoral head. After fully seating the femoral component, the appropriate modular head is impacted into the femoral neck. The hip is now ready to be reduced.
Presently, there are various hip replacement systems wherein a polymeric lining is used on the socket component. The metallic ball is received within this polymeric lining. The intention of the polymeric lining is to provide a very smooth and low friction movement between the metallic ball and the wall of the socket. Unfortunately, the repeated contact between the metallic surface of the ball member and the polymeric lining of the socket becomes worn over time. A need exists for being able to provide a lubricant into the space between the exterior surface of the ball member and the polymeric lining of the socket component. There is a general reluctance to use hydrocarbon-based lubricants in view of the potential incompatibility with the human body.
Other hip prosthesis have utilized polymeric linings located between a metallic shell and a metallic shaft of the stem portion of the prosthesis. The purpose of the lining is to allow the prosthesis to better conform to the movement of the human body and also to provide a cushioning effect between the metallic shell and the metal shell of the stem portion. It has been found that, over time, the polymeric lining within the stem portion can become worn so that replacement is required.
In the past, various patents have related to hip replacement operations and to hip prosthesis.
U.S. Pat. No. 3,748,662, issued on Jul. 31, 1973 to A. J. Helfet, describes a surgical procedure for replacing the natural components of a bicondylar joint in a human limb. The prosthetic implant has two pairs of coacting male and female condylar components. The male and female components which replace the natural lateral condyles are spherical or spheroidal in shape to simulate a ball and sock joint. Both male components and both female components can be formed on respective rigid carriers or they may optionally be separate for individual fixation to the patient""s limb.
U.S. Pat. No. 3,894,297, issued on Jul. 15, 1975 to Mittelmeier et al., describes a hip joint prosthesis which comprises a substantially frustoconical acetabulum member provided with supporting ribs in the form of a tapering thread and a prosthesis shaft provided with circular supporting ribs allowing anchorage of the prosthesis and the acetabulum member without using a cement or other adhesive.
U.S. Pat. No. 4,187,559, issued on Feb. 12, 1980 to Grell et al., describes a body joint endoprosthesis including an anchoring member having a shaft anchored in a first bone and a pivot member connected to the anchoring member by a pivot joint. The pivot member includes a first body joint member and a support element that bears against a seating surface of the first bone. The first body joint member and the second body joint member are connected to the second bone so as to form the body implant joint.
U.S. Pat. No. 4,355,427, issued on Oct. 26, 1982 to W. Schneider, describes an artificial humerus head having a groove in its exterior surface for receiving the long biceps tendon. A cover bridges the groove to form an elongated open-end channel for the tendon and makes it possible to arrange the long biceps tendon in the channel without separation thereof from the head.
U.S. Pat. No. 4,530,115, issued on Jul. 23, 1985 to Muller et al., describes a shank for a prosthesis which is composed of a blade which carries a joint head and a wedge-shaped end piece. The end piece is driven in along a guide in the lateral narrow side of the blade while the blade remains in a fixed position. The wedge-shaped form of the end piece permits fixation of the blade at a predetermined height such that the joint head can be at the level of the trochanter tip.
U.S. Pat. No. 4,775,381, issued on Oct. 4, 1988 to Tari et al., describes a hip prosthesis formed with a conventional head provided with a spherical shape, a neck, and a stem. A guide profile is formed along the outer straight side of the stem and contains components which are parallel with the side. The guide profile fits the inner surface of the medullary cavity nail so as to allow the simultaneous use of the hip prosthesis and the medullary cavity nail and the nailing of the already prosthetized femur.
U.S. Pat. No. 5,026,399, issued on Jun. 25, 1991 to Engelbrecht et al., describes a prosthetic device for the partial or total replacement of a bone, such as a femur. The prosthesis has a rod-like bridging member which spans the major part of the gap between the two joints. An abutment member is mounted at either end of the bridging member and each of the abutment members engages a bone adjacent that which is to be partially or totally replaced. Each of the abutment members may constitute part of an artificial joint. The abutment members may be rotatable relative to one another and to the bridging member about the longitudinal axis of the latter in order that the abutment members may assume a relative angular orientation best suited to the characteristics of the patient.
U.S. Pat. No. 5,702,457, issued on Dec. 30, 1997 to Walsh et al., describes a humeral prosthesis including a shank having a metaphyseal part having a housing therein with a semi-spherical portion in which housing is introduced a sphere to which is secured a bearing surface hemispherical cap adapted to be received within the glenoid cavity of a shoulder. A securing element is provided which extends through the metaphyseal part of the shank for securing the sphere within the housing at a predetermined position with respect to the shank.
U.S. Pat. No. 5,725,597, issued on Mar. 10, 1998 to S. K. Hwang, describes an artificial hip joint having a construction capable of reducing abrasion of a polyethylene layer formed within the acetabulum cup when the head of the femur pivots in the acetabulum cup. The artificial acetabulum cup is implanted in the acetabulum of a user""s pelvic bone and includes a hollow hemispherical member made of a metal. The polyethylene layer is formed on the inner surface of the hemispherical member. A femoral head holder is fixed to the femur. The femur head holder includes a spherical metal femur head pivotally held in the artificial acetabulum cup. A shaft is coupled at an upper end thereof to the femoral head and adapted to support the femoral head. A housing extends inclinedly through the greater trochanter of the femur and adapted to receive the shaft therein in such a manner that it rotates with respect to the shaft. Bearings are mounted between the shaft and the housing and are adapted to support axially and radial loads applied to the shaft at the femur head by the weight of the user.
It is an object of the present invention to provide a joint replacement system which is self-lubricating.
It is another object of the present invention to provide an hip replacement system which minimizes wear-and-tear between the ball component and the socket component.
It is another object of the present invention to provide an hip replacement system which allows the introduction of a human-based lubricant into the area between the ball component and the socket component.
It is still a further object of the present invention to provide a hip replacement system which allows lubricant to be introduced into the spaces located between metallic components and polymeric components of the hip replacement system.
It is a further object of the present invention to provide a hip replacement system which allows the human-based lubricant to be introduced, from time to time, into the system.
It is a further object of the present invention to provide a hip replacement system which maximizes the capability of the hip replacement system with the human body.
These and other objects and advantages of the present invention will become apparent from a reading of the attached specification and appended claims.
The present invention is a hip replacement system comprising a socket having a generally hemispherical cavity therein, a ball member cantably affixed within the socket and having an exterior surface positioned within the generally hemispherical cavity of the socket, a stem affixed to the ball member and extending outwardly therefrom, and a lubricant located within a channel formed in the stem. The exterior surface of the ball member has at least one opening therein communicating with an interior of the ball member. The stem has the channel in communication with this opening on the ball member.
In the preferred embodiment of the present invention, the lubricant is compressed body fat. This body fat extends through the channel so as to fill a space between the exterior surface of the ball member and an interior surface of the socket. An inlet is connected to the channel and extends outwardly of the stem. This inlet allows the lubricant to be introduced into the channel. The inlet is a catheter having a one-way valve secured thereto.
In the preferred embodiment of the present invention, the socket includes a metallic exterior body having an interior surface, and a polymeric lining affixed to the interior surface of the socket. The ball member is juxtaposed against the polymeric lining. A seal is affixed to the end of the socket for retaining the lubricant in the space between the exterior surface of the ball member and the interior surface of the socket. The seal is an annular gasket having an inner edge juxtaposed against the exterior surface of the ball member.
In the preferred embodiment of the present invention, the stem comprises a metallic shell, a polymeric lining extending along an interior surface of the metallic shell, and a metallic shaft positioned interior of the polymeric lining. The channel is formed between the shaft and the polymeric lining. A seal is affixed to the top of the shell for preventing the lubricant from passing outwardly from the stem. The shaft has a neck portion extending outwardly of the shell. The ball member is affixed to the neck portion. The channel will extend along the neck portion.
The socket is affixed within an acetabulum area of the human body. The stem is affixed within the femur of the human body. The lubricant is fat from the same human body.